European Search Report issued Sep. 11, 2007 in the International (PCT) Application of which the present application is the U.S. NationalStage. cited by other.

Abstract:

A light sensing area of a light sensing element is comprised of A1 region, A2 region, B1 region, B2 region and N region. A tilt detector carries out a tilt detection in accordance with a first difference signal, which is a difference signal between a signal obtained from the A1 region and a signal obtained from the B1 region, and a second difference signal, which is difference signal between a signal obtained from the A2 region and a signal obtained from the B2 region.Accordingly, an optical-disk tilt detecting signal having a little influence of defocusing can be obtained even at boundaries between recorded information tracks and non-recorded information tracks.

Claim:

What is claimed is:

1. An optical head, comprising a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, anda light sensing device for sensing a luminous flux reflected by information tracks, wherein: the light sensing device includes a luminous flux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axisof the objective lens and parallel with a direction tangent to the information tracks, straight first and second horizontal dividing lines normal to the vertical dividing line and symmetrically arranged with respect to the optical axis, a first and asecond partition lines symmetrically arranged between the two horizontal dividing lines with respect to the vertical dividing line while being distanced from the vertical dividing line and the two horizontal dividing lines, each of the first and secondpartition lines includes a pair of horizontal lines parallel with the two horizontal dividing lines, and an inner line connecting ends of the horizontal lines toward the vertical dividing line, the luminous flux incident area further includes an N regioncrossing over the vertical dividing line between the two horizontal dividing lines, one region partitioned between the two horizontal dividing lines by the vertical dividing line being divided into an A2 region at a side toward the optical axis and aremaining A1 region by the first partition line, and the other region partitioned between the two horizontal dividing lines by the vertical dividing line being divided into a B2 region at a side toward the optical axis and a remaining B1 region by thesecond partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A2 region and the B2 region are symmetrically arranged with respect to the vertical dividing line, and the optical headfurther comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident on the luminous flux incident area of the light sensing device.

2. An optical head according to claim 1, wherein the A1 region and the B1 regions are for mainly detecting a luminous energy in middle parts of sections where a 0.sup.th-order light and .+-.1.sup.st-order lights of the luminous flux overlap.

3. An optical head according to claim 2, wherein the A2 region and the B2 region are for mainly detecting a luminous energy in parts, excluding the middle parts, of the sections where the 0.sup.th-order light and the .+-.1.sup.st-order lightsof the luminous flux overlap.

4. An optical head according to claim 1, wherein the inner lines of the first and second partition lines are arcuate, and a ratio of the radius of curvature of the inner lines to the radius of the luminous flux is 0.5 or larger and 1.2 orsmaller.

5. An optical head according to claim 1, wherein: the light sensing device includes a light sensing element, on which the luminous flux incident area is provided, and the tilt detector detects the tilt in accordance with a first differencesignal, which is a difference signal between a signal obtained from the A1 region of the light sensing element and a signal obtained from the B1 region of the light sensing element, and a second difference signal, which is a difference signal between asignal obtained from the A2 region of the light sensing element and a signal obtained from the B2 region of the light sensing element.

6. An optical head according to claim 1, wherein: the light sensing device includes a light splitting element for slitting the luminous flux reflected by the information tracks into a plurality of luminous fluxes, and a light sensing elementfor separately sensing the respective luminous fluxes split by the light splitting element, the luminous flux incident area is provided on the light splitting element, and the tilt detector detects the tilt in accordance with a first difference signal,which is a difference signal between a signal obtained from the luminous flux diffracted in the A1 region of the light splitting element and detected by the light sensing element and a signal obtained from the luminous flux diffracted in the B1 region ofthe light splitting element and detected by the light sensing element, and a second difference signal, which is a difference signal between a signal obtained from the luminous flux diffracted in the A2 region of the light splitting element and detectedby the light sensing element and a signal obtained from the luminous flux diffracted in the B2 region of the light splitting element and detected by the light sensing element.

7. An optical head according to claim 1, wherein: the luminous flux incident area further includes an A3 region and a B3 region symmetrically arranged with respect to the vertical dividing line, the A3 region is defined as a region excludingthe N region, the A1 region and the A2 region from an area at a side of the vertical dividing line toward the A1 region, the B3 region is defined as a region excluding the N region, the B1 region and the B2 region from an area at a side of the verticaldividing line toward the B1 region, a difference signal between a signal obtained from the A3 region and a signal obtained from the B3 region serves as a third difference signal, and the optical head further comprises a tracking error signal generatorfor generating a tracking error signal in accordance with a sum signal of the first and second difference signal and the third difference signal.

8. An optical head, comprising a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensing a luminous flux reflected byinformation tracks, wherein: the light sensing device includes a luminous flux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent tothe information tracks, a first and a second partition lines symmetrically arranged with respect to the vertical dividing line while being distanced from the vertical dividing line, a third partition line arranged between the vertical dividing line andthe first partition line, a fourth partition line symmetrically arranged with the third partition line with respect to the optical axis between the vertical dividing line and the second partition line, each of the first and second partition linesincludes a pair of horizontal lines normal to the vertical dividing line, and an inner line connecting ends of the horizontal lines toward the vertical dividing line, each of the third and fourth partition lines includes a pair of horizontal lines normalto the vertical dividing line, and an inner line connecting ends of the horizontal lines toward the vertical dividing line, the luminous flux incident area further includes an N region crossing over the vertical dividing line, a region at a side of theoptical axis opposite from the third partition line being divided into an A5 region at a side toward the third partition line and a remaining A1 region by the first partition line, and a region at a side of the optical axis opposite from the fourthpartition line being divided into a B5 region at a side toward the fourth partition line and a remaining B1 region by the second partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A5region and the B5 region are symmetrically arranged with respect to the vertical dividing line, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminousenergy incident on the luminous flux incident area of the light sensing device.

9. An optical head according to claim 8, wherein the A1 region and the B1 regions are for mainly detecting a luminous energy in middle parts of sections where a 0.sup.th-order light and .+-.1.sup.st-order lights of the luminous flux overlap.

10. An optical head according to claim 9, wherein the A5 region and the B5 region are for mainly detecting a luminous energy in parts, excluding the middle parts, of the sections where the 0.sup.th-order light and the .+-.1.sup.st-order lightsof the luminous flux overlap.

11. An optical head according to claim 8, wherein any of the inner lines of the first to fourth partition lines is arcuate.

12. An optical head according to claim 11, wherein the inner lines of the third and fourth partition lines are both defined to have a radius of curvature equal to the radius of the luminous flux.

13. An optical head according to claim 8, wherein: the light sensing device includes a light sensing element, on which the luminous flux incident area is provided, and the tilt detector detects the tilt in accordance with a first differencesignal, which is a difference signal between a signal obtained from the A1 region of the light sensing element and a signal obtained from the B1 region of the light sensing element, and a second difference signal, which is a difference signal between asignal obtained from the A2 region of the light sensing element and a signal obtained from the B2 region of the light sensing element.

14. An optical head according to claim 8, wherein: the light sensing device includes a light splitting element for slitting the luminous flux reflected by the information tracks into a plurality of luminous fluxes, and a light sensing elementfor separately sensing the respective luminous fluxes split by the light splitting element, the luminous flux incident area is provided on the light splitting element, and the tilt detector detects the tilt in accordance with a first difference signal,which is a difference signal between a signal obtained from the luminous flux diffracted in the A1 region of the light splitting element and detected by the light sensing element and a signal obtained from the luminous flux diffracted in the B1 region ofthe light splitting element and detected by the light sensing element, and a second difference signal, which is a difference signal between a signal obtained from the luminous flux diffracted in the A2 region of the light splitting element and detectedby the light sensing element and a signal obtained from the luminous flux diffracted in the B2 region of the light splitting element and detected by the light sensing element.

15. An optical head according to claim 8, wherein: the luminous flux incident area further includes an A6 region and a B6 region symmetrically arranged with respect to the vertical dividing line, the A6 region is defined as a region excludingthe N region, the A1 region and the A5 region from an area at a side of the vertical dividing line toward the A1 region, the B6 region is defined as a region excluding the N region, the B1 region and the B5 region from an area at a side of the verticaldividing line toward the B1 region, a difference signal between a signal obtained from the A6 region and a signal obtained from the B6 region serves as a third difference signal, and the optical head further comprises a tracking error signal generatorfor generating a tracking error signal in accordance with a sum signal of the first and second difference signal and the third difference signal.

16. An optical head according to claim 8, wherein: a ratio of a dimension of the A5 region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.55 or larger and 0.65 or smaller, a ratio of a dimension of theB5 region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.55 or larger and 0.65 or smaller, a ratio of a dimension of the A1 region along the vertical dividing line to the diameter of the luminous flux to be sensedis 0.25 or larger and 0.35 or smaller, a ratio of a dimension of the B1 region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.25 or larger and 0.35 or smaller, a ratio of a distance between the A1 region and theB1 region to the diameter of the luminous flux to be sensed is 0.4 or larger and 0.5 or smaller, a ratio of a dimension the N region along a direction normal to the vertical dividing line to the diameter of the luminous flux to be sensed is 0.2 or largerand 0.4 or smaller, a ratio of the radius of curvature of the inner line of the first partition line to the radius of the luminous flux to be sensed is 0.5 or larger and 1.2 or smaller, and a ratio of the radius of the curvature of the inner line of thesecond partition line to the radius of the luminous flux to be sensed is 0.5 or larger and 1.2 or smaller.

17. An optical head, comprising a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensing a luminous flux reflected byinformation tracks, wherein: the light sensing device includes a luminous flux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent tothe information tracks, straight first and second horizontal dividing lines normal to the vertical dividing line and symmetrically arranged with respect to the optical axis, a third and a fourth horizontal dividing lines at a distance to and parallelwith the horizontal dividing lines in one region partitioned by the vertical dividing line between the first and second horizontal dividing lines, a fifth and a sixth horizontal dividing lines at a distance to and parallel with the horizontal dividinglines in the other region partitioned by the vertical dividing line, a seventh and an eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing lines opposite from the optical axis, in parallel with the first andsecond horizontal dividing lines and symmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the first and second horizontal dividing lines, a regionbetween the first and second horizontal dividing lines in the one region partitioned by the vertical dividing line is divided into an A1 region between the third and fourth horizontal dividing lines and remaining A7 regions, a region between the firstand second horizontal dividing lines in the other region partitioned by the vertical dividing line is divided into a B1 region between the fifth and sixth horizontal dividing lines and remaining B7 regions, regions at sides of the seventh and eighthhorizontal dividing lines opposite from the optical axis are defined as N2 regions, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A7 region and the B7 region are symmetrically arranged withrespect to the vertical dividing line, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident on the luminous flux incident area of thelight sensing device.

18. An optical head according to claim 17, wherein: the light sensing device further includes an A8 region and a B8 region symmetrically arranged with respect to the vertical dividing line in the luminous flux incident area, the A8 region isdefined as a region excluding the A1 region, the A7 region, the N region and the N2 regions from the one region partitioned by the vertical dividing line, and the B8 region is defined as a region excluding the B1 region, the B7 region, the N region andthe N2 regions from the other region partitioned by the vertical dividing line.

19. An optical head according to claim 18, wherein a difference signal between a signal obtained from the A8 region and a signal obtained from the B8 region serves as a third difference signal, and the optical head further comprises a trackingerror signal generator for generating a tracking error signal in accordance with a sum signal of the first and second difference signals and the third difference signal.

20. An optical head according to claim 17, wherein: a ratio of a dimension of the N region along a direction normal to the vertical dividing line to the diameter of the luminous flux to be sensed is 0.35 or larger and 0.45 or smaller, a ratioof a dimension of the N region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.5 or larger and 0.6 or smaller, a ratio of a dimension of the A1 region along the vertical dividing line to the diameter of theluminous flux to be sensed is 0.2 or larger and 0.32 or smaller, a ratio of a dimension of the B1 region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.2 or larger and 0.32 or smaller, and a ratio of a distancebetween the N2 regions to the diameter of the luminous flux to be sensed is 0.75 or larger and 0.85 or smaller.

21. An optical head, comprising a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensing a luminous flux reflected byinformation tracks, wherein: the light sensing device includes a luminous flux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent tothe information tracks; a pair of first horizontal dividing lines normal to the vertical dividing line and symmetrically arranged with respect to the vertical dividing line; a pair of second horizontal dividing lines parallel with the pair of firsthorizontal dividing lines and symmetrically arranged with respect to the vertical dividing line; a third and a fourth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in one region partitionedby the vertical dividing line between the first and second horizontal dividing lines; a fifth and a sixth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in the other region partitioned by thevertical dividing line between the first and second horizontal dividing lines; a first inner line extending in parallel with the vertical dividing line and connecting inner ends of the first horizontal dividing line at one side, the third horizontaldividing line, the fourth horizontal dividing line and the second horizontal dividing line at one side; a second inner line extending in parallel with the vertical dividing line and connecting inner ends the first horizontal dividing line at the otherside, the fifth horizontal dividing line, the sixth horizontal dividing line and the second horizontal dividing line at the other side; and seventh and eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing linesopposite from the optical axis, in parallel with the first and second horizontal dividing lines and symmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing linebetween the first and second inner lines, a region defined by the first horizontal dividing line, the second horizontal dividing line and the first inner line in the one region partitioned by the vertical dividing line is divided into an A1 regionbetween the third and fourth horizontal dividing lines and remaining A7 regions, a region defined by the first horizontal dividing line, the second horizontal dividing line and the second inner line in the other region partitioned by the verticaldividing line is divided into a B1 region between the fifth and sixth horizontal dividing lines and remaining B7 regions, regions at sides of the seventh and eighth horizontal dividing lines opposite from the optical axis are defined as N2 regions, thepair of first horizontal dividing lines and the pair of second horizontal dividing lines are symmetrically arranged with respect to the optical axis, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line,the A7 region and the B7 region are symmetrically arranged with respect to the vertical dividing line, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with aluminous energy incident on the luminous flux incident area of the light sensing device.

22. An optical head according to claim 21, wherein the A1 region and the B1 regions are for mainly detecting a luminous energy in middle parts of sections where a 0.sup.th-order light and .+-.1.sup.st-order lights of the luminous flux overlap.

23. An optical head according to claim 22, wherein the A7 region and the B7 region are for mainly detecting a luminous energy in parts, excluding the middle parts, of the sections where the 0.sup.th-order light and the .+-.1.sup.st-order lightsof the luminous flux overlap.

24. An optical head according to claim 21, wherein: the light sensing device further includes an A8 region and a B8 region symmetrically arranged with respect to the vertical dividing line in the luminous flux incident area, the A8 region isdefined as a region excluding the A1 region, the A7 region, the N region and the N2 regions from the one region partitioned by the vertical dividing line, and the B8 region is defined as a region excluding the B1 region, the B7 region, the N region andthe N2 regions from the other region partitioned by the vertical dividing line.

25. An optical head according to claim 24, wherein a difference signal between a signal obtained from the A8 region and a signal obtained from the B8 region serves as a third difference signal, and the optical head further comprises a trackingerror signal generator for generating a tracking error signal in accordance with a sum signal of the first and second difference signals and the third difference signal.

26. An optical head according to claim 21, wherein: a ratio of a dimension of the N region along a direction normal to the vertical dividing line to the diameter of the luminous flux to be sensed is 0.3 or larger and 0.4 or smaller, a ratio ofa dimension of the N region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.54 or larger and 0.65 or smaller, a ratio of a distance between the A1 region and the B1 region to the diameter of the luminous flux to besensed is 0.35 or larger and 0.45 or smaller, a ratio of a dimension of the A1 region along the vertical dividing line to the diameter of the luminous flux to be sensed is 0.25 or larger and 0.38 or smaller, a ratio of a dimension of the B1 region alongthe vertical dividing line to the diameter of the luminous flux to be sensed is 0.25 or larger and 0.38 or smaller, and a ratio of a distance between the N2 regions to the diameter of the luminous flux to be sensed is 0.8 or larger and 0.92 or smaller.

27. An optical head according to claim 17, wherein: the light sensing device includes a light sensing element, on which the luminous flux incident area is provided, and the tilt detector detects the tilt in accordance with a first differencesignal, which is a difference signal between a signal obtained from the A1 region of the light sensing element and a signal obtained from the B1 region of the light sensing element, and a second difference signal, which is a difference signal between asignal obtained from the A7 region of the light sensing element and a signal obtained from the B7 region of the light sensing element.

28. An optical head according to claim 18, wherein: the light sensing device includes a light sensing element, on which the luminous flux incident area is provided, and the tilt detector detects the tilt in accordance with a first differencesignal, which is a difference signal between a signal obtained from the A1 region of the light sensing element and a signal obtained from the B1 region of the light sensing element; a second difference signal, which is a difference signal between asignal obtained from the A7 region of the light sensing element and a signal obtained from the B7 region of the light sensing element; and a third difference signal, which is a difference signal between a signal obtained from the A8 region of the lightsensing element and a signal obtained from the B8 region of the light sensing element.

29. An optical head according to claim 17, wherein: the light sensing device includes a light splitting element for slitting the luminous flux reflected by the information tracks into a plurality of luminous fluxes, and a light sensing elementfor separately sensing the respective luminous fluxes split by the light splitting element, the luminous flux incident area is provided on the light splitting element, and the tilt detector detects the tilt in accordance with a first difference signal,which is a difference signal between a signal obtained from the luminous flux diffracted in the A1 region of the light splitting element and detected by the light sensing element and a signal obtained from the luminous flux diffracted in the B1 region ofthe light splitting element and detected by the light sensing element, and a second difference signal, which is a difference signal between a signal obtained from the luminous flux diffracted in the A7 region of the light splitting element and detectedby the light sensing element and a signal obtained from the luminous flux diffracted in the B7 region of the light splitting element and detected by the light sensing element.

30. An optical head according to claim 18, wherein: the light sensing device includes a light splitting element for slitting the luminous flux reflected by the information tracks into a plurality of luminous fluxes, and a light sensing elementfor separately sensing the respective luminous fluxes split by the light splitting element, the luminous flux incident area is provided on the light splitting element, and the tilt detector detects the tilt in accordance with a first difference signal,which is a difference signal between a signal obtained from the luminous flux diffracted in the A1 region of the light splitting element and detected by the light sensing element and a signal obtained from the luminous flux diffracted in the B1 region ofthe light splitting element and detected by the light sensing element; a second difference signal, which is a difference signal between a signal obtained from the luminous flux diffracted in the A7 region of the light splitting element and detected bythe light sensing element and a signal obtained from the luminous flux diffracted in the B7 region of the light splitting element and detected by the light sensing element; and a third difference signal, which is a difference signal between a signalobtained from the luminous flux diffracted in the A8 region of the light splitting element and detected by the light sensing element and a signal obtained from the luminous flux diffracted in the B8 region of the light splitting element and detected bythe light sensing element.

31. An optical head according to claim 5, wherein the tilt detector compares the first and second difference signals.

32. An optical head according to claim 5, wherein the tilt detector generates a difference signal between the first and second difference signals after multiplying at least one of the first and second difference signals by a specified weightcoefficient.

33. An optical head according to claim 5, wherein the tilt detector detects a signal based on the phases of the first and second difference signals or a phase difference between the first and second difference signals.

34. An optical head according to claim 1, wherein the optical disk is constructed such that light reflectivity differs at the information tracks having information recorded thereon and those having no information recorded thereon.

35. An optical disk device, comprising: an optical head including a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensinga luminous flux reflected by information tracks, an optical disk driver for driving the optical disk, and a controller for controlling the optical head and the optical disk driver, wherein: the light sensing device includes a luminous flux incident areadivided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, straight first and second horizontal dividing lines normal to thevertical dividing line and symmetrically arranged with respect to the optical axis, a first and a second partition lines symmetrically arranged between the two horizontal dividing lines with respect to the vertical dividing line while being distancedfrom the vertical dividing line and the two horizontal dividing lines, each of the first and second partition lines includes a pair of horizontal lines parallel with the two horizontal dividing lines, and an inner line connecting ends of the horizontallines toward the vertical dividing line, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the two horizontal dividing lines, one region partitioned between the two horizontal dividing lines bythe vertical dividing line being divided into an A2 region at a side toward the optical axis and a remaining A1 region by the first partition line, and the other region partitioned between the two horizontal dividing lines by the vertical dividing linebeing divided into a B2 region at a side toward the optical axis and a remaining B1 region by the second partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A2 region and the B2region are symmetrically arranged with respect to the vertical dividing line, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident onthe luminous flux incident area of the light sensing device.

36. An optical disk device, comprising: an optical head including a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensinga luminous flux reflected by information tracks, an optical disk driver for driving the optical disk, and a controller for controlling the optical head and the optical disk driver, wherein: the light sensing device includes a luminous flux incident areadivided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, a first and a second partition lines symmetrically arranged withrespect to the vertical dividing line while being distanced from the vertical dividing line, a third partition line arranged between the vertical dividing line and the first partition line, a fourth partition line symmetrically arranged with the thirdpartition line with respect to the optical axis between the vertical dividing line and the second partition line, each of the first and second partition lines includes a pair of horizontal lines normal to the vertical dividing line, and an inner lineconnecting ends of the horizontal lines toward the vertical dividing line, each of the third and fourth partition lines includes a pair of horizontal lines normal to the vertical dividing line, and an inner line connecting ends of the horizontal linestoward the vertical dividing line, the luminous flux incident area further includes an N region crossing over the vertical dividing line, a region at a side of the third partition line opposite from the optical axis being divided into an A5 region at aside toward the third partition line and a remaining A1 region by the first partition line, and a region at a side of the fourth partition line opposite from the optical axis being divided into a B5 region at a side toward the fourth partition line and aremaining B1 region by the second partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A5 region and the B5 region are symmetrically arranged with respect to the vertical dividingline, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident on the luminous flux incident area of the light sensing device.

37. An optical disk device, comprising: an optical head including a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensinga luminous flux reflected by information tracks, an optical disk driver for driving the optical disk, and a controller for controlling the optical head and the optical disk driver, wherein: the light sensing device includes a luminous flux incident areadivided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, straight first and second horizontal dividing lines normal to thevertical dividing line and symmetrically arranged with respect to the optical axis, a third and a fourth horizontal dividing lines at a distance to and parallel with the horizontal dividing lines in one region partitioned by the vertical dividing linebetween the first and second horizontal dividing lines, a fifth and a sixth horizontal dividing lines at a distance to and parallel with the horizontal dividing lines in the other region partitioned by the vertical dividing line between the first andsecond horizontal dividing lines, a seventh and an eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing lines opposite from the optical axis, in parallel with the first and second horizontal dividing lines andsymmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the first and second horizontal dividing lines, a region between the first and second horizontaldividing lines in the one region partitioned by the vertical dividing line is divided into an A1 region between the third and fourth horizontal dividing lines and remaining A7 regions, a region between the first and second horizontal dividing lines inthe other region partitioned by the vertical dividing line is divided into a B1 region between the fifth and sixth horizontal dividing lines and remaining B7 regions, regions at sides of the seventh and eighth horizontal dividing lines opposite from theoptical axis are defined as N2 regions, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A7 region and the B7 region are symmetrically arranged with respect to the vertical dividing line, and theoptical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident on the luminous flux incident area of the light sensing device.

38. An optical disk device, comprising: an optical head including a light source, an objective lens for concentrating a laser beam emitted from the light source onto information tracks of an optical disk, and a light sensing device for sensinga luminous flux reflected by information tracks, an optical disk driver for driving the optical disk, and a controller for controlling the optical head and the optical disk driver, wherein: the light sensing device includes a luminous flux incident areadivided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks; a pair of first horizontal dividing lines normal to the verticaldividing line and symmetrically arranged with respect to the vertical dividing line; a pair of second horizontal dividing lines parallel with the pair of first horizontal dividing lines and symmetrically arranged with respect to the vertical dividingline; a third and a fourth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in one region partitioned by the vertical dividing line between the first and second horizontal dividing lines; afifth and a sixth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in the other region partitioned by the vertical dividing line between the first and second horizontal dividing lines; a firstinner line extending in parallel with the vertical dividing line and connecting inner ends of the first horizontal dividing line at one side, the third horizontal dividing line, the fourth horizontal dividing line and the second horizontal dividing lineat one side; a second inner line extending in parallel with the vertical dividing line and connecting inner ends the first horizontal dividing line at the other side, the fifth horizontal dividing line, the sixth horizontal dividing line and the secondhorizontal dividing line at the other side; and seventh and eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing lines opposite from the optical axis, in parallel with the first and second horizontal dividinglines and symmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the first and second inner lines, a region defined by the first horizontal dividingline, the second horizontal dividing line and the first inner line in the one region partitioned by the vertical dividing line is divided into an A1 region between the third and fourth horizontal dividing lines and remaining A7 regions, a region definedby the first horizontal dividing line, the second horizontal dividing line and the second inner line in the other region partitioned by the vertical dividing line is divided into a B1 region between the fifth and sixth horizontal dividing lines andremaining B7 regions, regions at sides of the seventh and eighth horizontal dividing lines opposite from the optical axis are defined as N2 regions, the pair of first horizontal dividing lines and the pair of second horizontal dividing lines aresymmetrically arranged with respect to the optical axis, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A7 region and the B7 region are symmetrically arranged with respect to the verticaldividing line, and the optical head further comprises a tilt detector for detecting a relative tilt of the objective lens and the optical disk in accordance with a luminous energy incident on the luminous flux incident area of the light sensing device.

39. An integrated circuit for deriving a tilt signal corresponding to a relative tilt of an objective lens and an optical disk in accordance with a signal from a light sensing device of an optical head for concentrating a laser beam emittedfrom a light source onto information tracks of the optical disk by means of the objective lens and sensing a luminous flux reflected by the information tracks by means of the light sensing device, wherein: the light sensing device includes a luminousflux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, straight first and second horizontal dividing linesnormal to the vertical dividing line and symmetrically arranged with respect to the optical axis, a first and a second partition lines symmetrically arranged between the two horizontal dividing lines with respect to the vertical dividing line while beingdistanced from the vertical dividing line and the two horizontal dividing lines, each of the first and second partition lines includes a pair of horizontal lines parallel with the two horizontal dividing lines, and an inner line connecting ends of thehorizontal lines toward the vertical dividing line, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the two horizontal dividing lines, one region partitioned between the two horizontaldividing lines by the vertical dividing line being divided into an A2 region at a side toward the optical axis and a remaining A1 region by the first partition line, and the other region partitioned between the two horizontal dividing lines by thevertical dividing line being divided into a B2 region at a side toward the optical axis and a remaining B1 region by the second partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A2region and the B2 region are symmetrically arranged with respect to the vertical dividing line, and a difference signal between a first difference signal, which is a difference signal between a signal obtained from the A1 region of the light sensingdevice and a signal obtained from the B1 region of the light sensing device, and a second difference signal, which is a difference signal between a signal obtained from the A2 region of the light sensing device and a signal obtained from the B2 region ofthe light sensing device, is generated after multiplying at least one of the first and second difference signals by a specified weight coefficient, and the tilt signal is derived in accordance with the generated difference signal.

40. An integrated circuit according to claim 39, wherein the weight coefficient is so set as to reduce an offset in a difference signal produced as the objective lens is displaced.

41. An integrated circuit for deriving a tilt signal corresponding to a relative tilt of an objective lens and an optical disk in accordance with a signal from a light sensing device of an optical head for concentrating a laser beam emittedfrom a light source onto information tracks of the optical disk by means of the objective lens and sensing a luminous flux reflected by the information tracks by means of the light sensing device, wherein: the light sensing device includes a luminousflux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, a first and a second partition lines symmetricallyarranged with respect to the vertical dividing line while being distanced from the vertical dividing line, a third partition line arranged between the vertical dividing line and the first partition line, a fourth partition line symmetrically arrangedwith the third partition line with respect to the optical axis between the vertical dividing line and the second partition line, each of the first and second partition lines includes a pair of horizontal lines normal to the vertical dividing line, and aninner line connecting ends of the horizontal lines toward the vertical dividing line, each of the third and fourth partition lines includes a pair of horizontal lines normal to the vertical dividing line, and an inner line connecting ends of thehorizontal lines toward the vertical dividing line, the luminous flux incident area further includes an N region crossing over the vertical dividing line, a region at a side of the third partition line opposite from the optical axis being divided into anA5 region at a side toward the third partition line and a remaining A1 region by the first partition line, and a region at a side of the fourth partition line opposite from the optical axis being divided into a B5 region at a side toward the fourthpartition line and a remaining B1 region by the second partition line, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A5 region and the B5 region are symmetrically arranged with respect to thevertical dividing line, and a difference signal between a first difference signal, which is a difference signal between a signal obtained from the A1 region of the light sensing device and a signal obtained from the B1 region of the light sensing device,and a second difference signal, which is a difference signal between a signal obtained from the A5 region of the light sensing device and a signal obtained from the B5 region of the light sensing device, is generated after multiplying at least one ofthe first and second difference signals by a specified weight coefficient, and the tilt signal is derived in accordance with the generated difference signal.

42. An integrated circuit according to claim 41, wherein the weight coefficient is so set as to reduce an offset in a difference signal produced as the objective lens is displaced.

43. An integrated circuit for deriving a tilt signal corresponding to a relative tilt of an objective lens and an optical disk in accordance with a signal from a light sensing device of an optical head for concentrating a laser beam emittedfrom a light source onto information tracks of the optical disk by means of the objective lens and sensing a luminous flux reflected by the information tracks by means of the light sensing device, wherein: the light sensing device includes a luminousflux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks, straight first and second horizontal dividing linesnormal to the vertical dividing line and symmetrically arranged with respect to the optical axis, a third and a fourth horizontal dividing lines at a distance to and parallel with the horizontal dividing lines in one region partitioned by the verticaldividing line between the first and second horizontal dividing lines a fifth and a sixth horizontal dividing lines at a distance to and parallel with the horizontal dividing lines in the other region partitioned by the vertical dividing line between thefirst and second horizontal dividing lines, a seventh and an eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing lines opposite from the optical axis, in parallel with the first and second horizontal dividinglines and symmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the first and second horizontal dividing lines, a region between the first and secondhorizontal dividing lines in the one region partitioned by the vertical dividing line is divided into an A1 region between the third and fourth horizontal dividing lines and remaining A7 regions, a region between the first and second horizontal dividinglines in the other region partitioned by the vertical dividing line is divided into a B1 region between the fifth and sixth horizontal dividing lines and remaining B7 regions, regions at sides of the seventh and eighth horizontal dividing lines oppositefrom the optical axis are defined as N2 regions, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A7 region and the B7 region are symmetrically arranged with respect to the vertical dividing line,and a difference signal between a first difference signal, which is a difference signal between a signal obtained from the A1 region of the light sensing device and a signal obtained from the B1 region of the light sensing device, and a seconddifference signal, which is a difference signal between a signal obtained from the A7 region of the light sensing device and a signal obtained from the B7 region of the light sensing device, is generated after multiplying at least one of the first andsecond difference signals by a specified weight coefficient, and the tilt signal is derived in accordance with the generated difference signal.

44. An integrated circuit according to claim 43, wherein the weight coefficient is so set as to reduce an offset in a difference signal produced as the objective lens is displaced.

45. An integrated circuit for deriving a tilt signal corresponding to a relative tilt of an objective lens and an optical disk in accordance with a signal from a light sensing device of an optical head for concentrating a laser beam emittedfrom a light source onto information tracks of the optical disk by means of the objective lens and sensing a luminous flux reflected by the information tracks by means of the light sensing device, wherein: the light sensing device includes a luminousflux incident area divided into a plurality of regions by a straight vertical dividing line passing an optical axis of the objective lens and parallel with a direction tangent to the information tracks; a pair of first horizontal dividing lines normalto the vertical dividing line and symmetrically arranged with respect to the vertical dividing line; a pair of second horizontal dividing lines parallel with the pair of first horizontal dividing lines and symmetrically arranged with respect to thevertical dividing line; a third and a fourth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in one region partitioned by the vertical dividing line between the first and second horizontaldividing lines; a fifth and a sixth horizontal dividing lines at a distance to and parallel with the first and second horizontal dividing lines in the other region partitioned by the vertical dividing line between the first and second horizontaldividing lines; a first inner line extending in parallel with the vertical dividing line and connecting inner ends of the first horizontal dividing line at one side, the third horizontal dividing line, the fourth horizontal dividing line and the secondhorizontal dividing line at one side; a second inner line extending in parallel with the vertical dividing line and connecting inner ends the first horizontal dividing line at the other side, the fifth horizontal dividing line, the sixth horizontaldividing line and the second horizontal dividing line at the other side; and seventh and eighth horizontal dividing lines arranged at sides of the first and second horizontal dividing lines opposite from the optical axis, in parallel with the first andsecond horizontal dividing lines and symmetrically with respect to the optical axis, the luminous flux incident area further includes an N region crossing over the vertical dividing line between the first and second inner lines, a region defined by thefirst horizontal dividing line, the second horizontal dividing line and the first inner line in the one region partitioned by the vertical dividing line is divided into an A1 region between the third and fourth horizontal dividing lines and remaining A7regions, a region defined by the first horizontal dividing line, the second horizontal dividing line and the second inner line in the other region partitioned by the vertical dividing line is divided into a B1 region between the fifth and sixthhorizontal dividing lines and remaining B7 regions, regions at sides of the seventh and eighth horizontal dividing lines opposite from the optical axis are defined as N2 regions, the pair of first horizontal dividing lines and the pair of secondhorizontal dividing lines are symmetrically arranged with respect to the optical axis, the A1 region and the B1 region are symmetrically arranged with respect to the vertical dividing line, the A7 region and the B7 region are symmetrically arranged withrespect to the vertical dividing line, and a difference signal between a first difference signal, which is a difference signal between a signal obtained from the A1 region of the light sensing device and a signal obtained from the B1 region of the lightsensing device, and a second difference signal, which is a difference signal between a signal obtained from the A7 region of the light sensing device and a signal obtained from the B7 region of the light sensing device, is generated after multiplying atleast one of the first and second difference signals by a specified weight coefficient, and the tilt signal is derived in accordance with the generated difference signal.

46. An integrated circuit according to claim 45, wherein the weight coefficient is so set as to reduce an offset in a difference signal produced as the objective lens is displaced.